Nuclear reactor fuel element assemblies

ABSTRACT

A nuclear reactor fuel element assembly in which a plurality of sleeves arranged end to end house nuclear fuel-containing members arranged in clusters, wherein the ends of the fuel-containing members have cut-away portions or projections and the fuelcontaining members of the groups are so disposed that gravitational forces due to the weight of the fuel-containing members of the group, when the assembly is located in a vertical channel in a reactor core, act to produce couples on the members causing them to lean at one end towards one another in mutually supporting relationship and to lean at the other end away from one another against fixed surfaces provided at least in part by the walls of the sleeves.

States Pettinger et al.

' atet [451 May 16, 1972 [54] NUCLEAR REACTOR FUEL ELEMENT ASSEMBLIESThe Nuclear Power Group Limited, Knutsford, Cheshire, England [22]Filed: Oct. 28, 1968 [2]] Appl. No.: 771,035

[73] Assignee:

3,173,845 3/1965 Ritz ..176/75 X FOREIGN PATENTS OR APPLICATIONS 870,2636/1961 Great Britain 1 76/78 Primary Examiner-Carl D. QuarforthAssistant Examiner-Gary G. Solyst Attorney-Holman & Stern [5 7] ABSTRACTA nuclear reactor fuel element assembly in which a plurality of sleevesarranged end to end house nuclear fuel-containing members arranged inclusters, wherein the ends of the fuelcontaining members have cut-awayportions or projections and the fuel-containing members of the groupsare so disposed that gravitational forces due to the weight of thefuel-containing members of the group, when the assembly is located in avertical channel in a reactor core, act to produce couples on themembers causing them to lean at one end towards one another in mutuallysupporting relationship and to lean at the other end away from oneanother against fixed surfaces provided at least in part by the walls ofthe sleeves.

5 Claims, 4 Drawing Figures atented May 16, 1972 3,663,365

3 Sheets-Sho0t 15 Adam/70F DON/4L0 STANLEY PE777/V6El? ETAL NUCLEARREACTOR FUEL ELEMENT ASSEMBLIES This invention relates to nuclearreactor fuel element assemblies.

A known form of fuel element assembly used in high temperaturegas-cooled, graphite-moderated reactors comprises a plurality ofgraphite sleeves arranged end to end and spigotted together to form asubstantially continuous tube but capable of some degree of articulationat the joints between the sleeves.

Within the tube formed by the sleeves are located clusters offuel-containing tubes. The arrangement is such that when the assembly islocated in a vertical channel in the reactor core the sleeves supportone another and so do the fuel containers of adjacent sleeves.

The fuel-containing tubes are usually located in an annular space formedbetween the graphite sleeves and a centrally located tubular memberwhich may or may not contain nuclear fuel, the main purpose of thecentral member being to facilitate handling of the fuel element assemblywhen inserting the assembly in or removing it from the core.

Cooling gas flows through the tube formed by the graphite sleeves andover the surface of the fuel containing tubes which are in spacedrelation to one another.

In reactors where the cooling gas is at high pressure, forces due to gaspressure can set up vibration in the fuel-containing tubes with theconsequent danger of damage to the tubes and release of fissionproducts.

Rigid clamping of the fuel containing tubes can lead to difficulties asallowances must be made for differential expansion and shrinkage due toirradiation, and the clamping must not be such as to reduce thearticulation of the individual sleeves of the assembly.

The object of the present invention is to provide a nuclear reactor fuelelement assembly in which vibration of the fuel containing members iseliminated or reduced to negligible proportions without having to resortto clamping of any sort.

The invention consists in a nuclear reactor fuel element assemblycomprising a plurality of sleeves arranged end to end, said sleeveshousing nuclear fuel-containing members arranged in two or more axiallyspaced clusters, wherein fuelcontaining members of a cluster aresupported, when in position in a vertical channel in the reactor, byfuel-containing members of a cluster immediately below it, thefuel-containing members of a cluster being arranged in one or moregroups each group being associated with the fuel-containing members of acorresponding group of the cluster below, and wherein the ends of thefuel-containing members have cut-away portions or projections wherebyfor each pair of adjoining end faces, the end face of at least one ofthe fuel containing-mem bers has a cut-away portion or projection suchthat a vertical line joining the center of gravity of one member to theadjoining end faces passes outside the area of contact between the twoend faces, the fuel-containing members of the groups being so disposedthat gravitational forces due to the weight of the fuel-containingmembers of the group, when the assembly is located in a vertical channelin a reactor core, act to produce couples on the members causing them tolean at one end towards one another in mutually supporting relationshipand to lean at the other end away from one another against fixedsurfaces provided at least in part by the walls of the sleeves, thecouples acting on adjoining faces of fuel-containing members ofcorresponding groups in adjacent clusters acting to cause all themembers of both groups either to lean together or lean away from oneanother at the adjoining faces.

In one embodiment of the invention the fuel-containing members arelocated in groups in an annular space formed between the sleeves and acentrally located member, those ends of the members of a group leaningaway from one another being supported by the walls of the sleeves andbeing in mutually supporting relationship with fuel-containing membersof other groups of the cluster via the centrally located member.

To prevent relative rotation between members of a group lugs may beformed on each member which engage recesses or lugs on adjacent membersof the group. Where necessary the lugs may also abut surfaces or enterrecesses formed on the sleeves and/or the centrally located member. Thelugs may also act as spacing members between adjacent fuel-containingmembers of a cluster. The lugs may extend for the full length of thefuel containing members or extend only over the end portions thereof.

The invention also consists in a nuclear reactor fuel element assemblysubstantially as described herein with reference to the accompanyingdrawings in which:

FIG. 1 is a longitudinal section through part of a nuclear fuel elementassembly in accordance with one embodiment of the invention being asection on line AA of FIG. 2 which is an end view of the assembly shownin FIG. 1 looking in the direction of arrow B;

FIG. 3 is a section through one end of a nuclear fuel-containing memberused in the assembly shown in FIGS. 1 and 2; and

FIG. 4 is a diagrammatic view of part of an assembly in accordance withthe invention showing in exaggerated form the positions which thenuclear fuel containing members tend to take up.

In carrying the invention into effect in one form by way of example andreferring first of all to FIGS. 1 and 2 a nuclear fuel element assemblyis built up of a number of graphite sleeves of the kind shown at 1. Eachsleeve houses a cluster of nuclear fuel-containing members 2.

The members 2 are located in an annular space 3 formed between thesleeve 1 and a centrally located tubular member 4.

The members 2 are arranged in groups of three, a typical group beingshown at 2 2 and 2 Each member comprises essentially a tube housingnuclear fuel. The fuel can be located inside the tube or within itswalls as shown in FIG. 3 where the fuel is represented by referencenumeral 5.

Each member 2 has lugs 2a which abut against corresponding lugs onadjacent members of the group in which it is located to prevent relativerotation of the members.

The members may also have additional lugs 2b which serve to space themember from a member of an adjacent group or central member 4 or whichengage projections in on the wall of sleeve 1. The lugs 2a, 2b extendfor the full axial length of members 2 or for short distances at theends.

The lower end faces of the fuel-containing members 2, in the form shown,have cut-away portions or projections formed thereon which are off-setwith respect to the central axes of the members. In the followingdescription the term projection is used and is indicated by thereference numeral 20 in each case. The shape of the cross-section of theprojection can be seen from FIG. 2. Whilst in the form shown the upperend faces of the members do not carry oiT-set projections, suchprojections can be formed on the upper end faces if so desired.

The arrangement in accordance with the invention is best explained withreference to FIG. 4, in which is shown part of the annular channelformed between a stack of sleeves l in a fuel element assembly and acentrally located member 4 which may also consist of a number of tubularmembers arranged end to end as shown. The details of the joints betweensleeves and tubular members have not been shown as they form no part ofthe present invention.

For the purpose of explanation, the elements 2 and 2 of each group areassumed to lie in the plane of the drawing but when the elements are ingroups of three as shown in FIG. 2 it will be appreciated that this isnot the case in practice. The members 2 in the second sleeve from thetop of the drawing are disposed in the same manner as that shown inFIGS. 1 and 2. The projections 2c bear against flat end faces ofadjacent members 2 in a corresponding group of members in the cluster ofthe sleeve below.

Considering first of all the two adjacent sleeves in the middle of thedrawing, the gravitational forces due to the weights of the members inthe upper of the two sleeves act along a vertical line passing throughthe centers of gravity of the members. This vertical line passes outsidethe area of contact between adjacent members and the result is toproduce couples tending to cause the members to lean away from eachother as shown in exaggerated form.

The lateral forces acting at the joints between the end faces of themembers are taken up by the walls of the sleeves 1 and by members of anadjacent group (not shown) via the central member 4.

Considering now the upper pair of sleeves, the projections at the lowerend of the members 2 in the uppermost sleeve are disposed so that thegravitational forces acting exert couples tending to make the members 2lean against one another in mutually supporting relationship. Thus thefuel containing members of each group of a sleeve lean towards eachother at one end and away from each other at the other. The dispositionof the members and their respective projections is such that in adjacentsleeves the members of corresponding groups either all lean inward attheir adjoining faces or all lean outwards.

As mentioned earlier the members are shown displaced in an exaggeratedmanner in FIG. 4. In practice the members will be substantially verticalbut the couples acting thereon are such as to resist forces tending tovibrate the members.

Whilst in the above example fuel elements having graphite sleeves havebeen described, the use of graphite for the sleeves is not essential andother low neutron absorbing material such as silicon carbide can beused. The nuclear fuel-containing member may be of graphite or other lowneutron absorbing material.

A fuel element assembly such as that described, whilst particularlysuitable for gascooled graphite moderated reactors, can be used in anyreactor where the fuel element assembly is located in vertical channelsthrough which a cooling fluid is circulated.

1n the form described each cluster comprises a plurality of groups offuel-containing members but this is not essential. In some circumstancesa cluster may comprise only one group of members said group containingany number of members. It is not essential for each group to have thesame number of fuelcontaining members.

In the embodiments described a nuclear fuel-containing member is shownas a single member housing nuclear fuel but the term is used to includearrangements in which each member comprises a number of separateelements each containing nuclear fuel and each having a similar off-setprojection so that all the elements of a member tend to lean in the samedirection.

We claim:

1. A nuclear reactor fuel element assembly including a plurality ofsleeves disposed in end-to-end relationship with one another, aplurality of nuclear fuel-containing members, each member having endfaces, at least two axially spaced clusters of said nuclearfuel-containing members being disposed within said sleeves with saidfuel-containing members of one cluster being supported by saidfuel-containing members of a cluster immediately below it with adjacentend faces of said members in engagement, said fuel-containing members ofeach cluster defining at least one group, said group being coupled withsaid fuel-containing members of a corresponding group of the clusternext below, and wherein for each pair of engaging end faces of adjacentfuel-containing members, engagement means are disposed on at least oneend face, said engagement means being offset in position wherein avertical line joining the center of gravity of one member to theadjoining end faces passes outside the area of contact between the twoend faces, whereby said fuel-containing members of the groups are sodisposed that gravitational forces due to the weight of thefuelcontaining members of the group when the assembly is located in avertical channel in a reactor core, act to produce couples on themembers causing them to lean at one end towards one another in mutuallsupporting relationship and to lean at the other end away rom oneanother against fixed surfaces defined at least in part by the walls ofthe sleeves, the couples acting on adjoining faces of fuel-containingmembers of corresponding groups in adjacent clusters causing all themembers of both groups to lean in the same manner with respect to oneanother at the adjoining faces.

2. A fuel element assembly according to claim 1, wherein thefuel-containing member are located in groups in an annular space formedbetween the sleeves and a centrally located member, said sleeves havingwalls, those ends of the members of a group leaning away from oneanother contacting and being supported by said walls of the sleeves andcontacting and being in mutually supporting relationship withfuel-containing members of other groups of the cluster via saidcentrally located member.

3. A fuel-element assembly according to claim 1, wherein each member isfuel-element with lug-means engaging with engagement means on adjacentmembers of the group, thereby preventing relative rotation betweenmembers of the group.

4. A fuel element assembly according to claim 3, wherein the lug meansalso engage means on the sleeves.

5. A fuel element assembly according to claim 3, wherein the lug meansserve as spacing means between adjacent fuelcontaining member ofacluster.

2. A fuel element assembly according to claim 1, wherein thefuel-containing member are located in groups in an annular space formedbetween the sleeves and a centrally located member, said sleeves havingwalls, those ends of the members of a group leaning away from oneanother contacting and being supported by said walls of the sleeves andcontacting and being in mutually supporting relationship withfuel-containing members of other groups of the cluster via saidcentrally located member.
 3. A fuel-element assembly according to claim1, wherein each member is fuel-element with lug-means engaging withengagement means on adjacent members of the group, thereby preventingrelative rotation between members of the group.
 4. A fuel elementassembly according to claim 3, wherein the lug means also engage meanson the sleeves.
 5. A fuel element assembly according to claim 3, whereinthe lug means serve as spacing means between adjacent fuel-containingmember of a cluster.